JPH02194947A - Preparation of flexible metal clad laminated sheet - Google Patents

Abstract

PURPOSE:To prevent the curling of a polyimide film after a metal foil is removed by providing a polyimide layer easy to relieve stress between the metal foil and polyimide having a low coefficient of thermal expansion. CONSTITUTION:A solution of polyamide acid forming polyimide having a glass transition point of 320 deg.C or lower after the completion of imidating reaction is applied to a metal foil as the first layer and a solvent is removed to provide a polyamide acid layer. Subsequently, a solution of polyamide acid wherein the difference between the coefficient of thermal expansion of polyimide after the completion of imidating reaction and that of the metal foil becomes 1.5X10<-5>K<-1> or less is applied to the metal foil as the second layer and a solvent is removed to provide a polyamide acid layer. Thereafter, the imidating reactions of polyamide acids of the first and second layers are completed. That is, a solution containing 3-40wt.% of polyamide acid is emitted to the surface of the metal foil from a slit to be uniformly applied thereto. At this time, the width of the slit is adjusted so that the thickness of polyimide after the removal of a solvent and the completion of imidating reaction becomes 3-15mum to prepare the first layer. Next, the gap between a coater and the metal foil is adjusted so that the thickness of polyimide after the removal of a solvent and the completion of imidating reaction becomes 20-75mum to prepare the second layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a flexible metal-clad laminate.

[Conventional technology]

A flexible metal-clad laminate is a flexible laminate in which a metal foil is formed on the surface of a polymeric insulating film, and a flexible printed circuit board is formed by processing the metal foil of this laminate into a circuit. In recent years, this has been widely used as a means to achieve miniaturization and high density of electronic devices. Among these, those using aromatic polyimide as an insulating film are becoming mainstream.

Conventional flexible metal-clad laminates are manufactured by bonding polyimide film and copper foil with adhesive, so properties such as heat resistance, chemical resistance, flame retardance, electrical properties, and adhesion are not used. However, the excellent adhesive properties of polyimide cannot be fully utilized.

To solve this problem, a solution of polyamic acid (precursor of polyimide), which becomes polyimide with a coefficient of thermal expansion comparable to that of the metal foil, is directly cast onto the metal foil, and after the solvent is removed, imidization is performed. A method for manufacturing a flexible metal-clad laminate (hereinafter referred to as a direct coating method) has been proposed.

[Problem to be solved by the invention]

According to the above-mentioned direct coating method, not only the above-mentioned property deterioration caused by the adhesive can be solved, but also the manufacturing process can be greatly improved.
This allows for simple simplification.

However, in the flexible metal-clad laminate obtained by this method, when unnecessary conductors are removed after imidization and circuit formation is performed, the polyimide film curls toward the conductor foil side, which hinders subsequent work.

The present inventors have previously discovered that the cause of this curl is stress accompanying volumetric shrinkage of the polyimide film during solvent removal and imidization (curing).

Most of this stress can be alleviated by curing the flexible metal-clad laminate while fixing it in both the vertical and horizontal directions and by subjecting the resulting polyimide to a thermal history above its glass transition point. However, especially when using a low thermal expansion polyimide that has a coefficient of thermal expansion similar to that of metal foil, it is difficult for the polyimide molecular chains to flow at the adhesive interface between the metal foil and the polyimide film, making stress relaxation difficult. As a result, a residual stress layer is generated on the metal foil interface side of the polyimide film layer, and when unnecessary conductors are removed during circuit formation,
Stress in the polyimide film is released at that point, causing curling on the metal foil side.

The present invention provides a method for producing a flexible metal laminate in which the polyimide film is less curled even after the metal foil is removed, by a direct coating method with excellent workability.

[Means to solve the problem]

The present inventors have conducted intensive studies on a method for preventing curling of the polyimide film after removing the metal foil mentioned above, and have found that a material with a glass transition point of 320"C or less is used between the metal foil and the low thermal expansion polyimide. It was discovered that curling could be prevented by providing a polyimide layer that easily relaxes stress, and the present invention was completed.

That is, the present invention provides a method for producing a direct-coated flexible metal-clad laminate obtained by directly applying a polyamic acid solution to a metal foil, and then completing an imidization reaction after removing the solvent. The glass transition point of polyimide after completing the imidization reaction in the layer is 320.
A polyamic acid layer is formed by applying a solution of polyamic acid at a temperature below ℃ and removing the solvent.Then, the second layer is coated with a difference in thermal expansion coefficient of 1 between the polyimide and the metal foil after the imidization reaction is completed.
．． A solution of polyamic acid having a concentration of 11 or less is applied to 5 x 10 to 5, the solvent is removed to form a polyamic acid layer, and then the imidization reaction of the polyamic acid of the first layer and the second layer is completed. Features.

The present invention will be described in detail below. The polyimide that is finally formed on the metal foil is a polymer having repeating units represented by the following general formula (in this case, aromatic diamine, aromatic diisocyanate). It is a residue excluding an amino group or a cyanate group, and h is a residue excluding a carboxylic acid derivative portion of an aromatic tetracarboxylic acid derivative.

) R, as a diamine, diisocyanate is p
, m, o-phenylenediamine, 2.5-diaminotoluene, diaminodurene, benzidine, 4.4'-diaminoterphenyl, 4.4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, diaminodiphenyl sulfone, 2.2-bis(p-aminophenyl)propane, 3.3'-dimethylbenzidine, 3,3
'-dimethoxybenzidine, 3.3'-dimethyl-4,
4-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,4-bis(p-aminophenoxy)benzene, 4,4'-bis(
p-aminophenoxy)biphenyl, 2,2-bis(4
-(p-aminophenoxy)phenyl)propane, bis(4-(4-aminophenoxy)phenyl)sulfone,
or (Rs is a monovalent organic group, R4 is a divalent organic group, p is an integer of 1 or more) such as diamines such as diaminosiloxane, and diisocyanates obtained by reaction of these diamines with phosgene, etc. Aromatic diisocyanates include tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, diphenyl ether diisocyanate, and phenylene-1,3-diisocyanate.

Further, examples of the tetracarboxylic acid having R2 and its derivatives include the following. Although the tetracarboxylic acid is exemplified here, its esters, acid anhydrides, and acid chlorides can of course also be used. For example, pyromellitic acid, 2,3゜3',4'-tetracarboxydiphenyl, 3゜3',4,4'-tetracarboxydiphenyl, 3.3',4.4'-tetracarboxybenzophenone, 2, 3.3',4'-tetracarboxybenzophenone and the like.

Here, what is necessary for the polyimide to be provided as a stress relaxation layer on the upper layer of the metal foil is to molecularly design a system whose glass transition point after completion of the imidization reaction is 320° C. or lower. This is because stress relaxation of polyimide having a glass transition point higher than about 320° C. becomes difficult to occur, and the purpose of the layer as a stress relaxation layer cannot be achieved, and as a result, curling cannot be prevented.

On the other hand, what is important for the second layer of polyimide is to roughly match the thermal expansion coefficient of the polymer to that of the metal foil. For example, when using W4 foil as the metal foil, the average coefficient of thermal expansion of polyimide between 50°C and 250°C is set to 2 to prevent the board from curling.
The molecule is designed around X 10-5 K-', and the difference in thermal expansion coefficient with the metal foil is set to 1.5 X 10-sK-1 or less.

The synthesis reaction of polyamic acid involves N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DM
F), 0-200 in solutions such as N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), dimethyl sulfate, sulfolane, T-butyrolactone, cresol, phenol, halogenated phenol, dichlorohexanone, dioxane, etc. It is carried out in the range of °C.

The metal foil used in the present invention includes copper,
Examples include aluminum, iron, gold, silver, nickel, palladium, chromium, molybdenum, and alloys thereof.

The coefficient of thermal expansion of these metals is approximately 1.6 to 2.5
10-5K-'. In order to increase the adhesive strength with polyimide, mechanical or chemical treatment may be performed using corona discharge, sanding, plating, aluminum alcoholade, aluminum chelate, silane coupling agent, etc.

In the method of forming a polyimide film layer on metal foil in the present invention, first, a layer intended for stress relaxation is formed as a first layer. What is important here is to ensure that the polymer is not compatible with the polymer formed in the second layer and that the layers do not peel off. For example, if the layer contains 50% or more of a solvent, it will be miscible with the polymer in the second layer, making it impossible to achieve the purpose.

Furthermore, if the solvent removal and imidization reaction are carried out too much using a polyamic acid solution, peeling from the second layer polymer will occur. It is preferable to use a solution.

Specifically, a solution containing 3 to 40% by weight of polyamic acid is uniformly applied onto the surface of the metal foil by discharging it from a slint. At this time, the slit width is 3 to 15 μm, preferably 5 to 1 μm, and the thickness of polyimide after solvent removal and imidization reaction is completed.
Adjust so that it becomes 0 μm. Examples of this coating method include comma coater, knife coater, fountain coater, etc., but are not limited to these. Next, the polymer solvent is dried at 60 to 200°C, and the volatile content is adjusted to 10 to 40% by weight, preferably 20 to 30% by weight. If it is lower or higher than this, it may cause separation between the eyebrows or compatibility with the second layer polymer.

Next, apply the second layer in the same manner as the first layer.

The method involves removing the solvent from the gap between the coater and the metal conductor foil, and reducing the thickness of polyimide from 20 to 75 mm after the imidization reaction is completed.
It is the same as the first layer except that it is adjusted to µm.

Finally, this clad material is heated to 300 to 450°C to complete the imidization reaction.

The final temperature is important here. In other words, even if polyimide is formed as the second layer with a coefficient of thermal expansion that is almost the same as that of the metal foil, stress will occur due to solvent evaporation and imidization reaction during heating, and this stress will cause the laminate to warp or twist. be.

Most of these stresses can be alleviated by setting the final heating temperature to a temperature higher than the glass transition temperature of the polymer. In this way, a 23-90 μm polyimide film layer is formed on the metal foil.

Further, this step is preferably performed in an inert gas atmosphere in order to prevent oxidative corrosion of the conductor circuit and deterioration of the polyimide. Examples of the inert gas include helium, neon, argon, nitrogen, metal bright annealing gas, and mixed gases thereof. It is also possible to add a reducing gas such as hydrogen.

By providing the stress relaxation layer in this manner, it is possible to prevent the generation of residual stress that has conventionally occurred between the polyimide and the metal conductor foil, and to remove curls.

〔Example〕

Next, the present invention will be further explained based on examples.

The present invention is not limited to these.

Synthesis Example 1 30 with thermocouple, stirrer, and nitrogen inlet installed! p-phenylenediamine (hereinafter abbreviated as P-PDA) was introduced into a stainless steel reaction vessel while flowing dry nitrogen at a rate of 3001 d/min.
614.1g, 280.4g of 4,4'-diaminodiphenyl ether (hereinafter abbreviated as DDE) and 17k of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP).
g and stirred to dissolve P-PDA and DDE. While cooling this solution to below 20°C with a water jacket,
2105.4 g of 3°3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter abbreviated as BPDA) was gradually added and polymerized to obtain a viscous polyamic acid varnish. In order to improve the workability of subsequent coatings, the varnish was cured at 85° C. until the rotational viscosity of the varnish reached approximately 500 poise. This polyamic acid was formed into a polyimide film by a conventional method.

Its glass transition point is about 420℃, and the average coefficient of thermal expansion from 150℃ to 250℃ is 2. It was I x 10-5K-'.

Synthesis Example 2 1437.0 g of DDE as a diamine component and pyromellitic dianhydride (hereinafter referred to as P) as a tetracarboxylic dianhydride.
A polyamic acid varnish was obtained in the same manner as in Synthesis Example 1 except that 1563.0 g of MDA (abbreviated as MDA) was used. The glass transition point of the polyimide film obtained by heating this polyamic acid was 390'C.

Synthesis Example 3 1959.0 g of 2,2-bis(4-(4-aminophenoxy)phenyl)propane (hereinafter abbreviated as DAPP) as a diamine component and 1041.0 g of PMDA as a tetracarboxylic dianhydride. A polyamic acid varnish was obtained in the same manner as in Synthesis Example 1 except that Og was used. The glass transition point of the polyimide film obtained by heating this polyamic acid is 3.
It was 55℃.

Synthesis Example 4 A polyamic acid varnish was obtained in the same manner as in Synthesis Example 1 except that 1214.9 g of DDE and 1785.1 g of BPDA were used. The glass transition point of a polyimide film obtained by heating this polyamic acid with force was 285°C.

Synthesis Example 5 A polyamic acid varnish was obtained in the same manner as in Example 1, except that 1680.7 g of DAPP was used as the diamine component and 1319.3 g of benzophenone tetracarboxylic dianhydride (hereinafter abbreviated as BTDA) was used as the tetracarboxylic acid. . The glass transition point of the polyimide film obtained by heating this polyamic acid was 245°C.

Example 1 35μm electrolytic W4 foil (thermal expansion coefficient 1.68X10-5
K-1) was uniformly coated with the polyamic acid varnish obtained in Synthesis Example 4 using a coating machine to a final thickness of 10 μm, and dried at 160°C. The volatile content was 22.4%. Next, the polyamic acid varnish obtained in Synthesis Example 1 was applied thereon to a final thickness of 15 μm and dried. Next, this cladding material was heated in a continuous hardening furnace in a nitrogen atmosphere at a final temperature of 400° C. to convert the polyamic acid into polyimide to obtain a flexible metal clad N plate (hereinafter abbreviated as MCF). When the entire copper foil of this MCF was etched, no curl was observed in the polyimide film.

Comparative Example 1 The polyamic acid coated on the first layer was dried at a temperature of 100°C. The volatile content of this polyamic acid was 46.5%. Other than this, MCF was obtained in the same manner as in Example 1. In the obtained MCF, the polyamic acids of the first layer and the second layer were dissolved, and the obtained polyimide layer turned brown. Moreover, this polyimide film curled violently on the side that was clad with the copper foil. Its curvature is sxi
.

It was -”C’ll+-’.

Comparative Example 2 An MCF was obtained in the same manner as in Example 1 except that the same resin as in Example 1 was used and the final drying temperature of the polyamic acid coated on the - layer was 300°C. The volatile content of the first layer before coating the second layer of polyamic acid was 5.4%, and about 70% of the imidization reaction was completed.

The obtained MCF could not be used as an MCF because glabellar peeling occurred between the first and second layers.

Comparative Example 3 An MCF was obtained in the same manner as in Example 1, except that the polyamic acid synthesized in Synthesis Example 2 was used for the first layer. After etching out the entire surface of the copper, the polyimide film was severely curled and its curvature was 11 x 10-"clll-'.

curled violently. Its curvature is 9×】Q −
t cm −+. Example 2 An MCF was obtained in the same manner as in Example 1, except that the varnish synthesized in Synthesis Example 5 was used as the first layer polyamic acid. No curl was observed in the polyimide film after the entire copper foil of this MCF was etched out.

〔Effect of the invention〕

According to the present invention, it is possible to easily produce a flexible metal-clad laminate in which the polyimide film does not curl even after circuit processing, and its industrial value is extremely large.

Comparative example 4

Claims (1)

[Claims] 1. In the method for producing a direct-coated flexible metal-clad laminate obtained by directly applying a solution of polyamic acid to metal foil, then completing the imidization reaction after removing the solvent, imide is added to the first layer on the metal foil. After the imidization reaction is completed, a solution of polyamic acid whose glass transition point is 320°C or lower is applied, the solvent is removed, and a polyamic acid layer is provided.Then, the second layer is a metal foil of the polyimide after the imidization reaction is completed. The difference in thermal expansion coefficient is 1.5×10^-^
It is characterized by applying a solution of polyamic acid having a concentration of 5K^-^1 or less, removing the solvent to form a polyamic acid layer, and then completing the imidization reaction of the polyamic acid of the first layer and the second layer. Method for manufacturing flexible metal clad laminates.